I've been trying to culture some yeast from Erdinger bottles for a Hefe I want to brew tomorrow. My starter has been going since Monday night I think, but I'm not sure the starter I'm trying to make is ready.

How can I tell if I have enough yeast ?

Am I being unrealistic to think I can make a big enough starter this quickly ? How long should I expect to wait ?

Keep feeding the starter. Each time it drops the head, pour off the liquid and pour in more boiled cooled wort. You should start very small and work up to a 2 liter starter. Not using enough yeast you could have a failure in fermentation in your batch. I have done this before and you need to have patience. In the meanwhile you could brew using dried yeast. At least you will have beer.

Do not pour it out unless there has been no activity at all. If you read the link I posted you will see that they start with 10 ML of wort then 100ML, 1000ML etc. as steps. If you put a really tiny volume of yeast in a huge volume of wort it is nowhere as efficient. Swirl the yeast often to promote growth. Constant temperature of 70F also helps to get maximum growth. You always want to buy the freshest beer available to harvest yeast. Use several bottles and sanitary practices to avoid contamination. Sometimes it takes the better part of 2 weeks to make enough yeast.

Do you suppose I have enough yeast now ? The krausen on the starter rose and fell, I already stepped it up to 2 pints. Only thing is, I wonder if it might be infected ? Part of it looks like mold, even though it smells very yeasty - maybe a bit sour though...

This is essentually beer without hops so you can taste the beer and if it has no off flavors then it is fine. When you say mold, it is large bubbles of off color mass? Being sanitary with starters is of foremost importance.

Well sort of. Only its more solid looking. I smelled it - smells like yeast, but it does smell a little bit sour. I've seen something similar on top of my beer in the fermenter, but it looks very different than any other starter I've ever tried to make.

I did this with a 750 mL bottle over the course of 2 weeks and by the time I pulled it from the stir plate on brew day there was a ton of activity in the flask. HOWEVER, I was a bit nervous the first few days because I didn't see any activity. Keep in mind though, you're using VERY small quantities of wort and VERY few numbers of yeast cells so the activity won't be anything like that of a 5 gal batch.

Here's how I did it successfully (took 1.065 wort down to 1.004 in less than a week) and there's a great link in that page about the step by step process: http://brewingoutofbounds.blogspot.com